1 . Field of the Invention
The present invention relates to a lens barrel capable of correcting tracking data to correct an image plane variation.
2 . Description of the Related Art
Previously, in a lens barrel (a zoom optical system), since an image plane variation is generated in moving a lens unit to perform a magnification-varying operation, a control is performed so that a focus lens is moved to correct the image plane variation to maintain an in-focus state. A movement locus (a movement track) of the focus lens is previously defined as an electronic cam track (tracking data) that indicates a position of the focus lens with respect to a position of a moving lens unit for each object distance. In order to perform the magnification-varying operation while maintaining the in-focus state in this zoom optical system, it is necessary for the position of the moving lens unit and the position of the focus lens to exactly hold a relation defined by the tracking data.
However, when the position of the moving lens unit tries to be directly detected, reduction in size is prevented and cost is increased since a detector needs to be disposed near the zoom optical system. Therefore, a configuration of indirectly detecting the position of the moving lens unit is proposed, but a hysteresis is generated by the existence of a component of tracking delay such as a backlash or a flexure between the detector and the moving lens unit, and therefore the position of the moving lens unit cannot be exactly known.
Japanese Patent No. 4441018 discloses an optical apparatus capable of correcting a shift of an imaging plane even when a hysteresis exists in shooting using an optical system including the moving lens unit. This optical apparatus detects a hysteresis in zooming from a wide angle side to a telephoto side and from the telephoto side to the wide angle side, and corrects this hysteresis when a zoom direction is reversed.
The configuration of Japanese Patent No. 4441018 is effective when the hysteresis is uniform over an entire zoom range, i.e. when the hysteresis is uniform independently of a zoom position. However, actually, the hysteresis is different in accordance with the zoom position due to a flexure or a backlash of a part constituting a drive system or a configuration of a detection system. Therefore, in the configuration of Japanese Patent No. 4441018 , the influence of the hysteresis over the entire zoom range cannot be reduced.